1. The Field of the Invention
The invention generally relates to fiber-optic test equipment. More specifically, the invention relates to test equipment for testing optical transmitters and receivers used in fiber-optic communications.
2. Description of the Related Art
Fiber-optic networking can be used to communicate in modern high-speed networks. To transmit data on a fiber-optic network, the data must be converted from an electronic signal to an optical signal. This conversion may be done, for example, by using a transmitter or transmitting optical subassembly (TOSA). The transmitters and TOSAs often include light generating devices such as a laser or light emitting diode (LED). The light generating device is modulated according to digital data to produce a modulated optical signal.
When optical signals are received, those optical signals must generally be converted to an electronic signal. This is often accomplished using a receiver or a receiver optical subassembly (ROSA). Receivers and ROSAs generally include a photo sensitive device such as a photodiode connected to a transimpedance amplifier (TIA). When an optical signal impinges the photo sensitive device, a modulated current is induced in the photo sensitive device. This current can be converted by the TIA to an electronic signal usable by digital devices on a network.
Manufacturers of ROSAs and TOSAs typically perform various performance testing on the ROSAs and TOSAs before they are delivered to distributors and end customers. This performance testing can be used to detect defects or to sort components into groups of different rated values.
More particularly, testing directed towards the ROSA may include testing the responsivity of the ROSA to a modulated optical signal, testing the amount of current produced for a given amount of optical signal and so forth. Testing responsivity includes comparing a modulated optical signal input into the ROSA to an AC electrical signal produced by the ROSA as a result of receiving the AC optical signal.
Testing may be performed on the TOSA to characterize operating characteristics of the TOSA. One test that may be performed includes plotting the amount of optical energy produced by the TOSA as a function of the amount of current used to drive the TOSA. Another test includes measuring the amount of noise produced by the TOSA.
Many of these tests have conventionally been performed using expensive high-frequency test equipment. For example, some tests use a high frequency communications analyzer costing in the tens of thousands of dollars. Further, many of these test devices are general-purpose test devices. As such, these devices require excessive amounts of human interaction to perform the test result in and increase test times for each component. When each and every component manufactured is tested, this requires an inordinate amount of manpower and equipment to process testing of the components quickly.
Additionally, testing is often not repeatable from part to part. This is due to the changing nature of cables and the like associated with general purpose test equipment.